Planar cell polarity

[5] Planar cell polarity was first described in insects and then further defined in fruit flies (Drosophila melanogaster).

[5] There was a surge in interest in the Planar Cell Polarity pathway after conserved PCP genes were found to be involved in important vertebrate processes vertebrate gastrulation, mammalian ear patterning and hearing, and neural tube closure.

[5] Discoveries from this popular wave of PCP research has found its involvement in polarized ciliary beating in the trachea and brain ventricles,[7][8] oriented cell divisions,[9] lung branching,[10] and hair follicle alignment.

The core PCP genes in Drosophila and other vertebrates are Frizzled (Fz), Flamingo (Fmi), Strabismus (Stbm)/Van-gogh (Vang), Prickle (Pk), Dishevelled (Dsh), Diego (Dgo), and trimeric G protein Gαo.

Later research found that the function of the Frizzled (Fz) gene in Drosophila melanogaster is required to coordinate the cytoskeletons of epidermal cells to orient cuticular hairs and bristles on the surface of the insect.

However the core PCP proteins can function independent of β-catenin to result in downstream changes to cellular cytoskeleton and are known as a ‘‘noncanonical’’ Wnt pathway.

Through a feedback loop of the extracellular domains of Frizzled and Strabismus at the junctions of two neighboring cell membranes, the complex of Strabismus and Prickle and the complex of Frizzled and Disheveled and Diego are localized to opposite sides of the cells along the polarization axis.

Cartoon representation of Planar Cell Polarity in fly wing hair cells and mouse paw hair cells Figure 1. (A and B) Drosophila cuticular wing hair cells of the adult wing. Wing hairs point distally (to the right) in wild-type (WT) animals (A) but lose orientation in PCP mutants ( fz ) (B). (C and D) Hairs on the mouse paw point away from the body (pointing up) in WT (C) but grow in a swirling pattern in PCP mutants ( fz6 ) (D). Inspired by the work of Paul Adler (A and B) and Guo et al. (2004) (C and D).
Figure 2: Cartoon representation of Cuticular wing hair defect in Frizzled mutant flies.(A) The structure of Drosophila fly wing with and arrow showing the proximal and distal tips, (B) WT cuticular hairs in normal orientation towards the distal tip of the wing, (C) the disoriented cuticular hairs of the Frizzled( fz) mutant. The structures of the hairs are the same, only the orientation is different. Inspired by the work of David I. Strutt (2001)